Catalyst comprising a complex of a metal from subgroup VIII based on a bidentate phosphonite ligand, and method for producing nitriles

ABSTRACT

A catalyst which comprises at least one complex of a metal of subgroup VIII having at least one bidentate phosphonite ligand of the formula I                    
     or salts and mixtures thereof, a process for the preparation of mixtures of monoolefinic C 5 -mononitriles, a process for the catalytic isomerization of branched aliphatic monoalkenenitriles and a process for the preparation of adiponitrile.

This a 371 of PCT/EP99/03888 with international filing date of Jun. 4,1999.

The present invention relates to a catalyst which comprises a complex ofa metal of subgroup VIII, which comprises at least one bidentatephosphonite ligand, a process for the preparation of mixtures ofmonoolefinic C₅-mononitriles and a process for the preparation ofadipodinitrile by catalytic hydrocyanation in the presence of such acatalyst.

For the industrial production of polyamides, there is a considerabledemand worldwide for α,ω-alkylenediamines, which serve as an importantstarting material. α,ω-alkylenediamines, such as hexamethylenediamine,are obtained virtually exclusively by hydrogenating the correspondingdinitriles. Virtually all industrial routes for the production ofhexamethylenediamine are therefore essentially variants of theproduction of adipodinitrile, of which about 1.0 million metric tons areproduced annually worldwide.

K. Weissermel, H.-J. Arpe, Industrielle Organische Chemie, 4th edition,VCH Weinheim, page 266 et seq., describe four basically different routesfor the preparation of adipodinitrile, including the directhydrocyanation of 1,3-butadiene with hydrogen cyanide. In thelast-mentioned process, monoaddition in a first stage gives a mixture ofisomeric pentenenitriles, which is isomerized in a second stage to givepredominantly 3- and 4-pentenenitrile. Adipodinitrile is then formed ina third stage by an anti-Markownikow hydrogen cyanide addition reactionwith 4-pentenenitrile.

“Applied Homogeneous Catalysis with Organometalic Compounds”, Vol. 1,VCH Weinheim, page 465 et seq., describes in general the additionreaction of hydrogen cyanide with olefins under heterogeneous andhomogeneous catalysis. In particular, catalysts based on phosphine,phosphite and phosphinite complexes of nickel and of palladium are used.For the preparation of adipodinitrile by hydrocyanation of butadiene,predominantly nickel(0) phosphite catalysts are used, in the presence orabsence of a Lewis acid as a promoter.

J. Chem. Soc., Chem. Commun., 1991, page 1292, describes chiral aryldiphosphites as ligands for hydrocyanation catalysts. In these ligands,the phosphite group is bonded via two of its oxygen atoms to the 3- and3′-positions of a 2,2′-binaphthyl unit, with which it thus forms a7-membered heterocycle. In addition, two of these heterocycles maylikewise be linked via a 2,2′-binaphthyl unit to form a bidentatechelate ligand. In J. Chem. Soc., Chem. Commun., 1991, page 803 et seq.,analogous chelate diphosphite complexes of nickel(0) and platinum(0) aredescribed for this purpose, a 2,2′-biphenyl unit being used instead of a2,2′-binaphthyl unit as the bridging group.

U.S. Pat. No. 5,449,807 describes a process for the gas-phasehydrocyanation of diolefins in the presence of a supported nickelcatalyst based on at least one bidentate phosphite ligand, the twophosphite groups being bridged by an unsubstituted or substituted2,2′-biphenyl group. U.S. Pat. No. 5,440,067 describes a process for thegas-phase isomerization of 2-alkyl-3-monoalkenenitriles to give linear3- and/or 4-monoalkenenitriles in the presence of the catalystsdescribed in U.S. Pat. No. 5,449,807.

WO 95/14659 describes a process for the hydrocyanation of monoolefins,in which catalysts based on zero-valent nickel and bidentate phosphiteligands may be used. In these ligands, the phosphite groups togetherwith two of their oxygen atoms are part of an aryl-fused 7-memberedheterocycle. Pairs of these phosphite groups are then bridged byaryl-fused alkylene groups via the oxygen atoms which are not part ofthe heterocycle.

U.S. Pat. No. 5,512,695 likewise describes a process for thehydrocyanation of monoolefins in the presence of a nickel catalyst whichcomprises a bidentate phosphite ligand.

WO 96/11182 describes a process for hydrocyanation in the presence of anickel catalyst based on a bidentate or polydentate phosphite ligand inwhich the phosphite groups are not part of a heterocycle. The groupsused for bridging the phosphite groups correspond to those described inWO 95/14659.

U.S. Pat. No. 5,523,453 describes a process for hydrocyanation in thepresence of a nickel catalyst based on a bidentate ligand whichcomprises at least one phosphinite group and a furtherphosphorus-containing group which is selected from phosphinites andphosphites. The two phosphorus-containing groups of these bidentateligands are in turn bridged via aryl-fused groups. WO 97/23446 describesa process for the hydrocyanation of diolefins and for the isomerizationof 2-alkyl-3-monoalkenenitriles in the presence of catalysts whichcorrespond to those described in U.S. Pat. No. 5,523,453.

WO 96/22968 likewise describes a process for the hydrocyanation ofdiolefinic compounds and for the isomerization of the resulting,nonconjugated 2-alkyl-3-monoalkenenitriles, a nickel(0) catalyst basedon a polydentate phosphite ligand being used in the presence of a Lewisacid as promoter. The phosphite groups of these polydentate ligands areonce again components of aryl-fused heterocycles and may be bridged viaaryl-fused groups.

None of the abovementioned publications describes hydrocyanationcatalysts based on phosphonite ligands. In particular, no catalystsbased on bidentate chelate phosphonites are described.

U.S. Pat. No. 3,766,237 describes a process for the hydrocyanation ofethylenically unsaturated compounds which may have further functionalgroups, such as nitriles, in the presence of a nickel catalyst. Thesenickel catalysts carry four ligands of the formula M(X,Y,Z), where X, Yand Z, independently of one another, are each a radical R or OR and R isselected from alkyl and aryl groups of up to 18 carbon atoms. However,only phosphines and phosphites are mentioned explicitly and are used inthe examples for the hydrocyanation. On the other hand, it is notdisclosed that phosphonites can be used as ligands for nickel(0)hydrocyanation catalysts. In particular, no bidentate chelatephosphonite ligands are described.

It is an object of the present invention to provide novel catalystsbased on a metal of subgroup VIII. They should preferably have goodselectivity and good catalytic activity in the hydrocyanation of1,3-butadiene and 1,3-butadiene-containing hydrocarbon mixtures.Preferably, they should also be suitable for the catalytic isomerizationof monoalkenenitriles and for the addition reaction of the secondmolecule of hydrogen cyanide with said monoalkenenitriles, for examplefor the preparation of adipodinitrile.

We have surprisingly found that this object is achieved by catalystsbased on a metal of subgroup VIII which comprise at least one bidentatephosphonite ligand.

The present invention therefore relates to a catalyst comprising acomplex of a metal of subgroup VIII, having a bidentate phosphoniteligand of the formula I

where

A is a C₂- to C₇-alkylene bridge which may have 1, 2 or 3 double bondsand/or 1, 2 or 3 substituents which are selected from alkyl, cycloalkyland aryl, it being possible for the aryl substituent additionally tocarry 1, 2 or 3 substituents which are selected from alkyl, alkoxy,halogen, trifluoromethyl, nitro, alkoxycarbonyl and cyano, and/or theC₂- to C₇-alkylene bridge may be interrupted by 1, 2 or 3non-neighboring, unsubstituted or substituted heteroatoms, and/or theC₂- to C₇-alkylene bridge may be fused with one, two or three aryland/or hetaryl groups, it being possible for the fused aryl and hetarylgroups each to carry 1, 2 or 3 substituents which are selected fromalkyl, cycloalkyl, aryl, alkoxy, cycloalkoxy, aryloxy, acyl, halogen,trifluoromethyl, nitro, cyano, carboxyl, alkoxycarbonyl and NE¹E², whereE¹ and E² are identical or different and are each alkyl, cycloalkyl oraryl,

R¹ and R^(1′), independently of one another, are each alkyl, cycloalkyl,aryl or hetaryl, each of which may carry 1, 2 or 3 substituents whichare selected from alkyl, cycloalkyl and aryl,

R² and R^(2′), independently of one another, are each alkyl, cycloalkyl,aryl or hetaryl, it being possible for the aryl and hetaryl groups eachto carry 1, 2 or 3 substituents which are selected from alkyl,cycloalkyl, aryl, alkoxy, cycloalkoxy, aryloxy, acyl, halogen,trifluoromethyl, nitro, cyano, carboxyl, alkoxycarbonyl and NE¹E², whereE¹ and E² may have the abovementioned meanings,

or a salt or mixture thereof.

In the present invention, the term alkyl includes straight-chain andbranched alkyl groups. These are preferably straight-chain or branchedC₁-C₈-alkyl, preferably C₁-C₆-alkyl, particularly preferably C₁-C₄-alkylgroups. Examples of alkyl groups are in particular methyl, ethyl,propyl, isopropyl, n-butyl, 2-butyl, sec-butyl, tert-butyl, n-pentyl,2-pentyl, 2-methylbutyl, 3-methylbutyl, 1,2-dimethylpropyl,1,1-dimethylpropyl, 2,2-dimethylpropyl, 1-ethylpropyl, n-hexyl, 2-hexyl,2-methylpentyl, 3-methylpentyl, 4-methylpentyl, 1,2-dimethylbutyl,1,3-dimethylbutyl, 2,3-dimethylbutyl, 1,1-dimethylbutyl,2,2-dimethylbutyl, 3,3-dimethylbutyl, 1,1,2-trimethylpropyl,1,2,2-trimethylpropyl, 1-ethylbutyl, 2-ethylbutyl,1-ethyl-2-methylpropyl, n-heptyl, 2-heptyl, 3-heptyl, 2-ethylpentyl,1-propylbutyl and octyl.

The cycloalkyl group is preferably C₅-C₇-cycloalkyl, such ascyclopentyl, cyclohexyl or cycloheptyl.

If the cycloalkyl group is substituted, it preferably has 1, 2, 3, 4 or5, in particular 1, 2 or 3, substituents selected from alkyl, alkoxy,halogen or trifluoromethyl.

Aryl is preferably phenyl, tolyl, xylyl, mesityl, naphthyl, anthracenyl,phenanthrenyl or naphthacenyl, in particular phenyl or naphthyl. If thearyl group is substituted, it preferably has 1, 2, 3, 4 or 5,particularly preferably 1, 2 or 3, especially 1 or 2, substituents inany position.

Hetaryl is preferably pyridyl, quinolyl, acridinyl, pyridazinyl,pyrimidinyl or pyrazinyl.

Substituted hetaryl radicals preferably have 1, 2 or 3 substituentsselected from alkyl, alkoxy, halogen and trifluoromentyl.

The above statements on alkyl, cycloalkyl and aryl radicals areapplicable in a corresponding manner to alkoxy, cycloalkoxy and aryloxyradicals.

NE¹E² is preferably N,N-dimethyl, N,N-diethyl, N,N-dipropyl,N,N-diisopropyl, N,N-di-n-butyl, N,N-di-tert-butyl, N,N-dicyclohexyl orN,N-diphenyl.

Halogen is fluorine, chlorine, bromine or iodine, preferably fluorine orchlorine.

In the phosphonite ligands of the formula I, R¹ and R², and R^(1′) andR^(2′), are not linked to one another.

A is preferably a C₂-C₇-alkylene bridge which is fused with 1, 2 or 3aryl groups and which additionally may have a substituent which isselected from alkyl, cycloalkyl and unsubstituted and substituted aryland/or which additionally may be interrupted by an unsubstituted orsubstituted heteroarom.

The fused aryls of the radicals A are preferably benzene or naphthalene.Fused benzene rings are preferably unsubstituted or have 1, 2 or 3, inparticular 1 or 2, substituents which are selected from alkyl, alkoxy,halogen, trifluoromethyl, nitro, carboxyl, alkoxycarbonyl and cyano.Fused naphthalenes are preferably unsubstituted or have, in thenon-fused ring and/or in the fused ring, in each case 1, 2 or 3, inparticular 1 or 2, of the substituents mentioned above for the fusedbenzene rings. Fused naphthalenes which are substituted in the fusedring preferably have a substituent in the ortho position to thephosphonite group. This is then preferably alkyl or alkoxycarbonyl. Inthe case of the substituents of the fused aryls, alkyl is preferably C₁-to C₄-alkyl, in particular methyl, isopropyl or tert-butyl. Alkoxy ispreferably C₁-C₄-alkoxy, in particular methoxy. Alkoxycarbonyl ispreferably C₁- to C₄-alkoxycarbonyl. Halogen is in particular fluorineor chlorine.

If the C₂- to C₇-alkylene bridge of the radical A is interrupted by 1, 2or 3 unsubstituted or substituted heteroatoms, these are selected fromO, S or NR⁵, where R⁵ is alkyl, cycloalkyl or aryl. Preferably, the C₂-to C₇-alkylene bridge of the radical A is interrupted by anunsubstituted or substituted heteroatom.

If the C₂- to C₇-alkylene bridge of the radical A is substituted, it has1, 2 or 3 substituents, in particular 1 substituent, which is/areselected from alkyl, cycloalkyl and aryl, it being possible for the arylsubstituent additionally to carry 1, 2 or 3 substituents which areselected from alkyl, alkoxy, halogen, trifluoromethyl, nitro,alkoxycarbonyl and cyano. Preferably, the alkylene bridge A has onesubstituent which is selected from methyl, ethyl, isopropyl, phenyl orp-(C₁- to C₄-alkyl)phenyl, preferably p-methylphenyl or p-(C₁- toC₄-alkoxy)phenyl, preferably p-methoxyphenyl, p-halophenyl, preferablyp-chlorophenyl, and p-trifluoromethylphenyl.

Preferably, A is a C₄- to C₇-alkylene bridge which is fused and/orsubstituted and/or interrupted by unsubstituted or substitutedheteroatoms, as described above. In particular, A is a C₄- toC₅-alkylene bridge which is fused with one or two phenyl and/or naphthylgroups, it being possible for the phenyl or naphthyl groups to carry 1,2 or 3, in particular 1 or 2, of the abovementioned substituents.

In particular, A is a radical of the formulae II.1 to II.5

where

X is O, S or NR⁵, where

R⁵ is alkyl, cycloalkyl or aryl,

or X is a C₁- to C₃-alkylene bridge which may have a double bond and/oran alkyl, cycloalkyl or aryl substituent, it being possible for the arylsubstituent to carry 1, 2 or 3 substituents, which are selected fromalkyl, alkoxy, halogen, trifluoromethyl, nitro, alkoxycarbonyl andcyano,

or X is a C₂- or C₃-alkylene bridge which is interrupted by O, S or NR⁵,

and R³, R^(3′), R^(3″), R^(3′″), R⁴, R^(4′), R^(4″) and R^(4′″),independently of one another, are each hydrogen, alkyl, alkoxy, halogen,trifluormethyl, nitro, alkoxycarbonyl or cyano.

Preferably, A is a radical of the formula II.1, where R³ and R⁴ are eachhydrogen.

Preferably, A is a radical of the formula II.2a

where

R³ is hydrogen or C₁- to C₄-alkyl, preferably methyl, isopropyl ortert-butyl, and

R⁴ is hydrogen, C₁- to C₄-alkyl, preferably methyl, isopropyl ortert-butyl, C₁- to C₄-alkoxy, preferably methoxy, fluorine, chlorine ortrifluoromethyl.

Preferably, A is a radical of the formula II.3a

where

R³ and R⁴ have the meanings mentioned above in the case of the formulaII.2a and

R⁹ is hydrogen, C₁- to C₄-alkyl, preferably methyl or ethyl, phenyl,p-(C₁- to C₄-alkoxy)phenyl, preferably p-methoxyphenyl, p-fluorophenyl,p-chlorophenyl or p-(trifluoromethyl)phenyl.

Preferably, A is a radical of the formula II.4, where R³, R^(3′),R^(3″), R^(3′″), R⁴, R^(4′), R^(4″) and R^(4′″) are each hydrogen.

Preferably, A is a radical of the formula II.4, where R³, R^(3′), R⁴,R^(4′), R^(4″) and R^(4′″) are each hydrogen and R^(3″) and R^(3′″),independently of one another, are each alkoxycarbonyl, preferablymethoxycarbonyl, ethoxycarbonyl, n-propoxycarbonyl orisopropoxycarbonyl. In particular, R^(3″) and R^(3′″) are ortho to thephosphonite group.

Preferably, A is a radical of the formula II.5, where R³, R^(3′),R^(3″), R^(3′″), R⁴, R^(4′), R^(4″) and R^(4′″) are each hydrogen and Xis CR⁹, where R⁹ has the abovementioned meanings.

Preferably, A is a radical of the formula II.5, where R³, R^(3′), R⁴,R^(4′), R^(4″) and R^(4′″) are each hydrogen, X is CR⁹ and R^(3″) andR^(3′″), independently of one another, are each alkoxycarbonyl,preferably methoxycarbonyl, ethoxycarbonyl, n-propoxycarbonyl orisopropoxycarbonyl. In particular, R^(3″) and R^(3′″) are ortho to thephosphonite group.

In the formula I, R¹ and R^(1′), independently of one another, arepreferably alkyl or aryl, in particular phenyl, 1-naphthyl or2-naphthyl.

Preferably, R² and R^(2′), independently of one another, are each phenylwhich may carry 1 or 2 substituents which are selected from alkyl,alkoxy, halogen, trifluoromethyl, nitro, cyano, alkoxycarbonyl orcarboxyl.

In a preferred embodiment, the phosphonite ligand of the formula I isselected from ligands of the formulae Ia to Ic

where in the formula Ia R³, R⁴, R⁷ and R⁸ have the following meanings:

R³ R⁴ R⁷ R⁸ H H H H tert-butyl methyl H H tert-butyl methoxy H H H Hmethyl H H H ethyl H H H isopropyl H H H tert-butyl H H Cl H H H CF₃ H HH H methyl methoxy

in the formula Ib R⁴, R⁷, R⁸ and R⁹ have the following meanings:

R⁴ R⁷ R⁸ R⁹ H H H H Cl H H H methoxy H H H H H H phenyl H methyl H H Hmethyl methoxy H H methyl methoxy phenyl

in the formula Ic R⁷ and R⁸ have the following meanings:

R⁷ R⁸ H H methyl H ethyl H isopropyl H tert-butyl H methyl methoxyisopropyl H isopropyl methoxy H Cl H CF₃

The present invention furthermore relates to phosphonite ligands of theformula I

as defined above, where

R² and R^(2′), independently of one another, are each alkyl, cycloalkyl,aryl or hetaryl, it being possible for the aryl and hetaryl groups eachto carry 1 or 2 substituents which are selected from alkyl, cycloalkyl,aryl, alkoxy, cycloalkoxy, aryloxy, acyl, halogen, trifluoromethyl,nitro, cyano, carboxyl, alkoxycarbonyl and NE¹E^(2′) where E¹ and E² maybe identical or different and are each alkyl, cycloalkyl or aryl.

R² and R^(2′), independently of one another, are preferably each phenylwhich may carry 1 or 2 of the abovementioned substituents.

The novel catalysts may have one or more of the phosphonite ligands ofthe formula I. In addition to the ligands of formula I which aredescribed above, they may also have at least one further ligand which isselected from cyanide, halides, amines, carboxylates, acetylacetone,arylsulfonates, alkanesulfonates, hydride, CO, olefins, dienes,cycloolefins, nitrites, N-containing heterocycles, aromatics andheteroaromatics, ethers, PF₃ and mono-, bi- and polydentate phosphine,phosphinite, phosphonite and phosphite ligands. These further ligandsmay likewise be mono-, bi- or polydentate and may have coordinate bondsto the metal of subgroup VIII. Suitable further phosphorus-containingligands are, for example, the phosphine, phosphinite and phosphiteligands described above as prior art.

Preferably, the metal of subgroup VIII is cobalt, rhodium, ruthenium,palladium or nickel. If the novel catalysts are used for hydrocyanation,the metal of subgroup VIII is in particular nickel.

For the preparation of the phosphonite ligands of the formula I whichare used in the novel catalysts, a dihalophosphorus(III) compound III,where R¹ (or R^(1′)) has the abovementioned meanings, can first bereacted with a monoalcohol IV, where R² (or R^(2′)) has theabovementioned meanings, to give a compound of the formula V, accordingto the following scheme. If desired, this compound V can be isolatedand/or purified by known methods, e.g. by distillation, before thefurther reaction. The compound V is then reacted with a diol of theformula VI to give the bidentate phosphonite ligands of the formula (I).Where, in the formula (I), R¹ is identical to R_(1′) and R² is identicalto R^(2′), two equivalents of the formula V can be reacted with oneequivalent of the formula VI in a one-stage reaction. Otherwise, firstone equivalent of the formula V is reacted with one equivalent of theformula VI and, after formation of the monocondensate, a second compoundof the formula (V) Cl-PR^(1′)—OR^(2′) is added and is further reacted togive the phosphonite of the formula (I).

The compound of the formula (III) is preferably adichlorophosphorus(III) compound. Suitable compounds having theabovementioned radicals R¹ are known. If, for example, R¹ is phenyl, thecompound is dichlorophenylphosphine.

Suitable alcohols of the formula IV, where R² has the abovementionedmeanings, are likewise known. Suitable aromatic alcohols of the formulaHOR² are, for example, 2-tert-butyl-4-methylphenol, 2-isopropylphenol,2-tert-butylphenol, 4-tert-butylphenol,2,6-di-tert-butyl-4-methylphenol, 2,4-di-tert-butylphenol,2,6-di-tert-butylphenol, 2,4-dimethylphenol, 2,5-dimethylphenol,2,6-dimethylphenol, 3,4-dimethylphenol, 3,5-dimethylphenol,2-ethylphenol, 3-ethylphenol, 4-ethylphenol, 5-isopropyl-2-methylphenol,m-cresol, o-cresol, p-cresol, 1-naphthol, 2-naphthol, phenol,1-bromo-2-naphthol, 3-bromophenol, 5-chloroquin-8-ol,4-chloro-3,5-dimethylphenol, 2-chloro-5-methylphenol,4-chloro-3-methylphenol, 2-chloro-6-nitrophenol, 2-chlorophenol,3-chlorophenol, 4-chlorophenol, 4-chlororesorcinol, 2,3-dichlorophenol,2,4-dichlorophenol, 2,5-dichlorophenol, 2,6-dichlorophenol,3,4-dichlorophenol, 2-fluorophenol, 3-fluorophenol, 4-fluorophenol,3-methyl-4-nitrophenol, 3-isopropyl-4-nitrophenol,3-isopropyl-4-nitrophenol, 2-nitroanisole, 4-nitropyrocatechol,2-nitrophenol, 3-nitrophenol, 2-methoxy-3-methylphenol,2-methoxy-4-methylphenol, 2-methoxyphenol, 3-methoxyphenol and4-methoxyphenol. Preferred alcohols of the formula HOR¹ are2-isopropylphenol, 2,6-di-tert-butyl-4-methylphenol,2,4-di-tert-butylphenol, 2,6-di-tert-butylphenol, phenol,2-fluorophenol, 3-fluorophenol, 4-fluorophenol, 4-nitropyrocatechol,2-methoxy-4-methylphenol, 2-trifluoromethylphenol,3,5-bis(trifluoromethyl)phenol, 4-cyanophenol, etc.

Suitable alcohols of the formula HO—A—OH, where A has the abovementionedmeanings, are known. These include, for example, biphenyl-2,2′-diol andbinaphthyl-2,2′-diol. Further suitable diols are mentioned in U.S. Pat.No. 5,312,996, column 19, which is hereby expressly incorporated byreference.

Both the reaction of the compound (III) with (IV) to give (V) and thefurther reaction to give the bidentate phosphonite ligands of theformula (I) take place in general at elevated temperatures of from about40 to about 200° C. Both reactions can be carried out in the presence ofa base, for example an aliphatic amine, such as diethylamine,propylamine, dibutylamine, trimethylamine, tripropylamine or preferablytriethylamine or pyridine. The elimination of hydrogen halide ispreferably effected purely thermally in the first reaction step.

Advantageously, the preparation of the phosphonite ligands of theformula I which are used according to the invention is effected withoutusing organomagnesium or organolithium compounds. The simple reactionsequence permits a wide variation of the ligands. The preparation isthus carried out efficiently and economically from readily availablestarting materials.

For the preparation of the novel catalysts, at least one phosphoniteligand of the formula I can be reacted with a metal of subgroup VIII,e.g. nickel, or with a compound of the metal in the presence of areducing agent or a complex of the metal, in each case in an inertsolvent. Suitable nickel compounds of, for example, compounds in whichthe transition metal assumes an oxidation state higher than 0 and whichare reduced in situ during the reaction with the phosphonite ligand ofthe formula I, in the presence or absence of a suitable reducing agent.These include, for example, the halides, preferably the chlorides, andthe acetates of the abovementioned transition metals. NiCl₂ ispreferably used. Suitable reducing agents are, for example, metals,preferably alkali metals, such as Na and K, aluminum, zinc andtrialkylaluminum compounds.

If complex compounds of the transition metal are themselves used for thepreparation of the phosphonite-nickel(0) complexes, the transition metalis preferably already in the zero-valent state in said complexcompounds. Preferably, complexes having ligands which correspond to theabovementioned, additional ligands of the novel complexes are used forthe preparation. In this case, the preparation is carried out by partialor complete ligand exchange with the phosphonite ligands of the formula(I) which are described above.

The nickel complex bis(1,5-cyclooctadienyl)nickel(0) is preferred.

Suitable inert solvents for the preparation of the nickel(0) complexesare, for example, aromatics, such as benzene, toluene, ethylbenzene andchlorobenzene, ethers, preferably diethyl ether and tetrahydrofuran, andhaloalkanes, for example dichloromethane, chloroform, dichloroethane andtrichloroethane. Other suitable solvents are the liquid startingmaterials and/or products of the catalyzed reaction. The temperature isfrom −70 to 150° C., preferably from 0° C. to 100° C., particularlypreferably about room temperature.

If elemental nickel is used for the preparation of thephosphonite-nickel(0) complexes, it is preferably in the form of apowder. The reaction of nickel and phosphonite ligand is preferablyeffected in a product of the catalyzed reaction, such as thehydrocyanation reaction, as the solvent, for example in a mixture ofmonoolefinic C₅-mononitriles or, preferably, in 3-pentenenitrile or2-methyl-3-butenenitrile. If required, the ligand may also be used assolvent. The temperature is from about 0 to 150° C., preferably 60 to100° C.

The molar ratio of metal of subgroup VIII to bidentate phosphoniteligand is preferably from about 1:1 to 1:5, particularly preferably from1:1 to 1:3.

The present invention furthermore relates to a process for thepreparation of mixtures of monoolefinic C₅-mononitriles having anonconjugated C═C and C≡N bond by catalytic hydrocyanation of butadieneor of a 1,3-butadiene-containing hydrocarbon mixture, wherein thehydrocyanation is carried out in the presence of at least one of thenovel catalysts described above.

For the preparation of mixtures of monoolefinic C₅-mononitriles whichcontain, for example, 3-pentenenitrile and 2-methyl-3-butenenitrile andwhich are suitable as intermediates for further processing to giveadipodinitrile, pure butadiene or 1,3-butadiene-containing hydrocarbonmixtures may be used.

If a hydrocarbon mixture is used in the novel process, said mixture hasa 1,3-butadiene content of at least 10, preferably at least 25, inparticular at least 40, % by volume.

1,3-Butadiene-containing hydrocarbon mixtures are available on anindustrial scale. Thus, a hydrocarbon mixture referred to as a C₄ cutand having a high total olefin fraction is obtained, for example, in theworking-up of mineral oil by steam cracking of naphtha, about 40% ofsaid fraction being accounted for by 1,3-butadiene and the remainder bymonoolefins and polyunsaturated hydrocarbons as well as alkanes. Thesestreams always also contain small amounts of in general up to 5% ofalkynes, 1,2-dienes and vinylacetylene.

Pure 1,3-butadiene can be isolated from industrially availablehydrocarbon mixtures, for example by extractive distillation.

C₄ cuts are, if required, essentially freed from 1,2-dienes, such aspropadiene, and from alkenynes, e.g. vinylacetylene, before thehydrocyanation of alkynes, such as propyne or butyne. Otherwise,products may be obtained in which a C═C double bond is present inconjugation with the C≡N bond. These may act as catalyst poisons for thefirst reaction step of the adipic acid preparation, the monoadditionreaction of hydrogen cyanide.

If required, those components which may give rise to catalyst poisons,in particular alkynes, 1,2-dienes and mixtures thereof, are thereforepartially or completely removed from the hydrocarbon mixture. To removethese components, the C₄ cut is subjected to a partial catalytichydrogenation before the addition reaction with hydrogen cyanide. Thispartial hydrogenation is effected in the presence of a hydrogenationcatalyst which is capable of hydrogenating alkynes and 1,2-dienesselectively alongside other dienes and monoolefins.

Suitable heterogeneous catalyst systems for the selective hydrogenationare known and comprise in general a transition metal compound on aninert support. They are in particular those described in U.S. Pat. Nos.4,587,369, 4,704,492 and 4,493,906, which are hereby fully incorporatedby reference. Further suitable catalyst systems based on copper are soldby Dow Chemical as KLP catalyst.

The addition reaction of hydrogen cyanide with 1,3-butadiene or with1,3-butadiene-containing hydrocarbon mixture, for example a pretreated,partially hydrogenated C₄ cut, can be carried out continuously,semicontinuously or batchwise.

Suitable reactors for the reaction are known to a person skilled in theart and are described, for example, in Ullmanns Enzyklopädie dertechnischen Chemie, Vol. 1, 3rd edition, 1951, page 743 et seq. and page769 et seq. Preferably, a stirred catalyst cascade or a tube reactor isused for a continuous process.

If the addition reaction of the hydrogen cyanide with 1,3-butadiene orwith a 1,3-butadiene-containing hydrocarbon mixture is carried outsemicontinuously or batchwise, for example, an autoclave which, ifdesired, can be provided with a stirring apparatus and an internallining is used for the novel process.

A suitable semicontinuous process comprises:

a) Filling a reactor with 1,3-butadiene or with the hydrocarbon mixture,if required, a part of the hydrogen cyanide and a novel hydrocyanationcatalyst which may have been produced in situ and, if required, asolvent. Suitable solvents are those mentioned above for the preparationof the novel catalysts, preferably aromatic hydrocarbons, such astoluene or xylene, or tetrahydrofuran.

b) Reaction of the mixture at elevated temperatures and superatmosphericpressure. The reaction temperature is in general from about 0 to 200°C., preferably from about 50 to 150° C. The pressure is in general fromabout 1 to 200 bar, preferably from about 1 to 100, in particular from 1to 50, particularly preferably from 1 to 20, bar. During the reaction,hydrogen cyanide is fed in at the rate at which it is consumed.

c) If required, completion of the reaction by continued reaction andsubsequent working up. To complete the reaction, the reaction time maybe followed by a subsequent reaction time of from 0 minutes to about 5hours, preferably from about 1 hour to 3.5 hours, in which hydrogencyanide is no longer fed into the autoclaves. The temperature is leftessentially constant at the previously set reaction temperature duringthis time. Working up is effected by conventional methods and comprisesthe removal of the unconverted 1,3-butadiene and of the unconvertedhydrogen cyanide, for example by washing or extraction, and working-upof the remaining reaction mixture by distillation to isolate the desiredproducts and recover the still active catalyst.

In a further suitable variant of the novel process, the additionreaction of the hydrogen cyanide with the 1,3-butadiene-containinghydrocarbon mixture is carried out batchwise. Essentially the reactionconditions described in the semicontinuous process are maintained, noadditional hydrogen cyanide being fed in in step b) but hydrogen cyanidebeing completely initially taken.

The addition reaction of the hydrogen cyanide with 1,3-butadiene or a1,3-butadiene-containing hydrocarbon mixture is preferably carried outcontinuously. The reaction is generally carried out so that essentiallyno relatively large amounts of unconverted hydrogen cyanide are presentin the reactor. Suitable processes for the continuous hydrocyanation areknown to a person skilled in the art. They include, for example, a feedprocess in which 1,3-butadiene and hydrocyanic acid are fed to a reactorvia separate feeds at the rate at which they are consumed. The catalystscan be fed in together with one of the starting materials or via aseparate feed. Suitable, preferably thoroughly mixable reactors arelikewise known to a person skilled in the art. They include, forexample, stirred catalysts, catalytic cascades and tube reactors, which,if required, are provided with an internal lining. The working-up of thereaction products, too, is preferably carried out by a conventionalcontinuous method.

In general, the 3-pentenenitrile/2-methyl-3-butenenitrile ratio obtainedin the monoaddition reaction of hydrogen cyanide with 1,3-butadiene orthe 1,3-butadiene-containing hydrocarbon mixture immediately after theend of the addition reaction (unconverted hydrogen cyanide no longerpresent) is at least 0.4:1. Advantageously, an isomerizationadditionally takes place at higher reaction temperatures and/or duringlonger reaction times in the presence of the novel catalysts, the3-pentenenitrile/2-methyl-3-butenenitrile ratio obtained then generallybeing about 2:1, preferably about 5:1, in particular about 8:1.

In general, the preparation of adipodinitrile from butadiene or from abutadiene-containing hydrocarbon mixture by addition of 2 molarequivalents of hydrogen cyanide can be divided into three steps:

1. Preparation of C₅-monoolefin mixtures having a nitrile function.

2. Isomerization of the 2-methyl-3-butenenitrile contained in thesemixtures to give 3-pentenenitrile and isomerization of the3-pentenenitrile thus formed and of the 3-pentenenitrile alreadycontained from step 1 to give various n-pentenenitriles. A very highfraction of 3-pentenenitrile or 4-pentenenitrile and a very smallfraction of conjugated 2-pentenenitrile and 2-methyl-2-butenenitrilewhich may act as a catalyst poison should be formed.

3. Preparation of adipodinitrile by an addition reaction of hydrogencyanide with the 3-pentenenitrile formed in step 2 and isomerizedbeforehand “in situ” to 4-pentenenitrile.

The novel catalysts based on phosphonite ligands are also advantageousfor the positional and double bond isomerization in step 2 and/or theaddition reaction of the second molecule of hydrogen cyanide in step 3.

The present invention therefore furthermore relates to a process for thecatalytic isomerization of branched aliphatic monoalkenenitriles havinga nonconjugated C═C and C≡N bond to give linear monoalkenenitriles,wherein the isomerization is carried out in the presence of a novelcatalyst.

Suitable branched aliphatic monoalkenenitriles are preferably acyclic,aliphatic, nonconjugated 2-alkyl-3-monoalkenenitriles and in particular2-methyl-3-butenenitrile. Mixtures of monoolefinic C₅-mononitriles, asobtainable by the process, described above, for the catalytichydrocyanation of butadiene or of 1,3-butadiene-containing hydrocarbonmixtures, are preferably used for the isomerization. Advantageously, thenovel catalysts exhibit good activity with respect to the formation oflinear monoalkene nitrites. The isomerization can, if desired, beeffected in the presence of a conventional promoter, for example a Lewisacid, such as AlCl₃ or ZnCl₂. Advantagously, the novel catalystsgenerally permit isomerization without the addition of a promoter. Theselectivity of the novel catalysts in the isomerization without theaddition of a promoter is in general higher than that with the additionof a promoter. Furthermore, expensive removal of the promoter of theisomerization can be dispensed with. Thus, in principle only onecatalyst circulation for hydrocyanation, isomerization and, if required,an addition reaction of a second molecule of hydrogen cyanide isrequired. Dispensing with the promoter and simplification of the processwhich is possible in principle generally permit a reduction of the costscompared with known processes.

The temperature in the isomerization is from about 50 to 160° C.,preferably from 70 to 130° C.

The present invention furthermore relates to a process for thepreparation of adipodinitrile by catalytic hydrocyanation of linearmonoolefinic C₅-mononitriles, wherein the hydrocyanation is carried outin the presence of a novel catalyst. Advantageously, a mixture ofmonoolefinic C₅-mononitriles which is obtainable by the novel processfor the catalytic hydrocyanation of butadiene or of a1,3-butadiene-containing hydrocarbon mixture and which, if required, wasadditionally subjected to working up and/or to isomerization by thenovel isomerization process described above is used for thehydrocyanation. In a suitable embodiment of the novel process, thehydrocyanation of the monoolefinic C₅-mononitriles is carried out in thepresence of a promoter, for example a Lewis acid, such as AlCl₃, ZnCl₂,BF₃, B(C₆H₅)₃, SnCl₄, Sn(C₆H₅)₃OSO₂CF₃, etc.

In a suitable embodiment of the novel process for the preparation ofadipodinitrile, the catalytic hydrocyanation of butadiene or of a1,3-butadiene-containing hydrocarbon mixture (Step 1) and theisomerization (Step 2) are carried out in the manner of a one-potreaction without isolation of the hydrocyanation products.Hydrocyanation and isomerization can be carried out, for example, in onereactor, the reaction temperature being increased, if required, afterthe end of the hydrogen cyanide addition. Hydrocyanation andisomerization can also be carried out in separate reactors, where, forexample, after the end of the monoaddition reaction of hydrogen cyanidein a first reactor, the catalyst-containing reaction mixture istransferred, without isolation and working up, to a second reactor andis isomerized therein.

In a further suitable embodiment of the novel process, all three stepsof the adipodinitrile preparation, i.e. preparation of monoolefinicC₅-mononitriles, isomerization and addition of the second molecule ofhydrogen cyanide, are carried out in the manner of a one-pot reaction.

The present invention therefore relates to a process for the preparationof adipodinitrile, comprising

a) preparation of a mixture of monoolefinic C₅-mononitriles having anonconjugated C═C and C≡N bond by catalytic hydrocyanation of butadieneor of a 1,3-butadiene-containing hydrocarbon mixture,

b) catalytic isomerization of the mixture from a), and

c) catalytic hydrocyanation of the isomerized mixture from b), whereinthe steps a), b) and c) are carried out in the presence of at least onenovel catalyst and without isolation of the product or products fromstep a) and/or b).

The novel catalysts can be prepared simply and thus economically fromreadily obtainable intermediates, some of which are commerciallyavailable. Advantageously, they have high activity and good selectivitywith respect to the monoadducts or isomerization products obtained inthe hydrocynation of 1,3-butadiene-containing hydrocarbon mixtures. Ingeneral, they have higher stability relative to hydrogen cyanide thanconventional hydrocyanation catalysts and, in the hydrocyanation, anexcess of hydrogen cyanide can also be added to said catalysts withoutresulting in marked deposition of inactive nickel(II) compounds, e.g.nickel(II) cyanide. In contrast to known hydrocyanation catalysts basedon non-complex phosphine and phosphite ligands, the novel catalysts aretherefore suitable not only for continuous hydrocyanation processes inwhich an excess of hydrogen cyanide in the reaction mixture cangenerally be effectively avoided but also for semicontinuous processesand batch processes in which a large excess of hydrogen cyanide isgenerally present. Thus, the catalysts used according to the inventionand the hydrocyanation processes based on them generally have highercatalyst recycling rates and longer catalyst on-stream times than knownprocesses. This is advantageous not only for achieving bettercost-efficiency but also from ecological points of view, since thenickel cyanide formed from the active catalyst with hydrogen cyanide ishighly toxic and must be worked up or disposed of at high cost.Moreover, in the preparation of the novel catalysts, generally no excessor a smaller excess of ligand is required relative to the metal ofsubgroup VIII than in the case of conventional catalysts.

In addition to the hydrocyanation of 1,3-butadiene-containinghydrocarbon mixtures, the catalysts of the formula I are generallysuitable for all conventional hydrocyanation processes. In particular,the hydrocyanation of nonactivated olefins, for example of styrene and3-pentenenitrile, may be mentioned.

The catalysts which are described above and comprise chiral phosphoniteligands of the formula I are suitable for enantioselectivehydrocyanation.

The nonrestricting examples which follow illustrate the invention.

EXAMPLES

The following ligand I was used in Examples 1 and 3 and the ligand IIwas used in Examples 2 and 4:

Example 1

(According to the Invention)

Semicontinuous Hydrocyanation of 1,3-butadiene

0.41 g (1.5 mmol) of bis(1,5-cyclooctadienyl)nickel(0), 2.14 g of ligandI and 10 ml of toluene are initially taken under argon at roomtemperature in a glass autoclave and stirred for 10 minutes, thereaction batch acquiring a red-brown color. A mixutre of 7.9 g (146mmol) of 1,3-butadiene and 40 g of toluene is then added. The glassautoclave is tightly closed and the reaction mixture is heated to 70°C., an initial pressure of 1.2 bar being established. A mixture of 3.2 g(118 mmol) of freshly distilled hydrocyanic acid in 40 g of toluene iscontinuously metered in over a period of 90 minutes. Thereafter, thepressure has fallen to 0.5 bar. The reaction is then completed in thecourse of a further 120 minutes at about 70° C. Toluene is used forwashing the reaction discharge. The course of the reaction is monitoredby pressure and temperature measurement.

In a subsequent Volhard cyanide determination, hydrogen cyanideconversion of more than 99% is determined.

GC analysis (column: 30 m Stabil-Wachs, temperature program: 5 minutesisothermally at 50° C., then heating up at a rate of 5° C./min at 240°C., gas chromatograph: Hewlett Packard HP 5890) with internal standard(benzonitrile): 99.4% of 3-pentenenitrile, 4-pentenenitrile and2-methyl-3-butenenitrile, based on hydrogen cyanide used.

3-Pentenenitrile: 2-methyl-3-butenenitrile ratio=0.41:1

As shown in the following Example 2, the ratio of 3-pentenenitrile to2-methyl-3-butenenitrile is shifted in favor of 3-pentenenitrile byprolonging the reaction time beyond the end of the hydrogen cyanideaddition. The addition of a promoter is not necessary.

Example 2

(According to the Invention)

Semicontinuous Hydrocyanation of 1,3-butadiene with Isomerization

0.41 g (1.5 mmol) of bis(1,5-cyclooctadienyl)nickel(0), 2.9 g of ligandII and 10 g of toluene are initially taken under an argon atmosphere atroom temperature in a glass autoclave and stirred for 10 minutes, thereaction batch acquiring a red-brown color. A mixture of 8.1 g (150mmol) of 1,3-butadiene and 40 g of toluene is then added. The glassautoclave is tightly closed and the reaction mixture is heated to 90° C.A mixture of 4.0 g of freshly distilled hydrocyanic acid in 40 g oftoluene is metered in continuously over a period of 90 minutes. Afterthe end of the addition, the temperature is increased to 110° C. Thecourse of the isomerization (ratio of 3-pentenenitrile to2-methyl-3-butenenitrile) is investigated at regular intervals (0, 3, 6,22 h) by means of GC analysis, as described in Example 1. The resultsare shown in Table 1.

TABLE 1 Time after end of addition 3-Pentenenitrile: [h]2-methyl-3-butenenitrile ratio 0 0.27:1 3 1.94:1 6 4.75:1 22  8.25:1

Since, owing to the taking of samples for gas chromatography, an exactdetermination of the yield was not possible, the same batch was runagain without sampling. There was no subsequent reaction time.

Yield: 99.6%

3-Pentenenitrile: 2-methyl-3-butenenitrile ratio=0.22:1 (Determinationof yield: see Example 1)

Example 3

(According to the Invention)

Isomerization of 2-methyl-3-butenenitrile to 3-pentenenitrile

0.72 g of ligand I, 15 ml of toluene and 0.14 g (0.5 mmol) ofbis(1,5-cyclooctadienyl)nickel(0) are initially taken under an argonatmosphere and stirred at room temperature for 45 minutes. The catalystcomplex which forms is precipitated from the initially homogeneoussolution. The volatile components are removed at highly superatmosphericpressure. 40.5 g (500 mmol) of 2-methyl-3-butenenitrile are added to theremaining solid. The solution is heated to 110° C. The course of thereaction is investigated at regular intervals by means of a gaschromatograph. The product ratio after a reaction time of 300 minutes isshown in Table 2. All products and by-products shown there were assignedbeforehand by means of gas chromatography, GC-MS, GC-MS-IR and NMR. Allvalues are in GC percent by area.

Weight of sample: 1.0160 g

Weight of standard: 1.4416 g

TABLE 2 Product ratio after a reaction time of 300 minutes CompoundAmount [GC % by area] trans-2-methyl-2-butenenitrile 0.982-methyl-3-butenenitrile 7.41 trans-2-pentenenitrile 0cis-2-methyl-2-butenenitrile 0.21 4-pentenenitrile 0.33trans-3-pentenenitrile 43.10 cis-3-pentenenitrile 1.32methylglutaronitrile 0.14 benzonitrile (standard) 45.55 Conversion:71.65% Selectivity: >99% (Note: The starting material itself containsabout 1% of cis- and trans-2-methyl-2-butenenitrile)

As demonstrated by Example 3, isomerization using the novel catalysts isalso possible without the addition of a promoter.

Example 4

(According to the Invention)

An Isomerization of 2-methyl-3-butenenitrile to 3-pentenenitrile

0.39 g of ligand II, 8 ml of toluene and 0.07 g (0.25 mmol) ofbis(1,5-cyclooctadienyl)nickel(0) are initially taken under an argonatmosphere and stirred at room temperature for 30 minutes. Some of thecatalyst complex which forms is precipitated from the initially redhomogeneous solution. The volatile components are removed at highlysuperatmospheric pressure. 20.2 g (250 mmol) of 2-methyl-3-butenenitrileare added to the remaining solid. The solution is heated to 125° C. Thecourse of the reaction is investigated at regular intervals by means ofa gas chromatograph. The product ratio after a reaction time of 300minutes is shown in Table 3. All products and by-products shown therewere assigned beforehand by means of gas chromatography, GC-MS, GC-MS-IRand NMR. All values are in GC percent by area.

Weight of sample: 1.2109 g

Weight of standard: 1.00262 g

TABLE 3 Product ratio after a reaction time of 300 minutes CompoundAmount [GC % by area] trans-2-methyl-2-butenenitrile 3.872-methyl-3-butenenitrile 2.16 trans-2-pentenenitrile 0.36cis-2-methyl-2-butenenitrile 1.43 4-pentenenitrile 1.31trans-3-pentenenitrile 38.20 cis-3-pentenenitrile 3.60methylglutaronitrile 0 benzonitrile (standard) 47.95 Conversion: 95.74%

We claim:
 1. A catalyst composition comprising a complex of a metal ofgroup VIII, and a bidentate phosphonite ligand of the formula I

where A is a C₂- to C₇-alkylene bridge which may have 1, 2 or 3 doublebonds and/or 1, 2 or 3 substituents which are selected from alkyl,cycloalkyl and aryl, it being possible for the aryl substituentadditionally to carry 1, 2 or 3 substituents which are selected fromalkyl, alkoxy, halogen, trifluoromethyl, nitro, alkoxycarbonyl andcyano, and/or the C₂- to C₇-alkylene bridge may be interrupted by 1, 2or 3 non-neighboring, unsubstituted or substituted heteroatoms, and/orthe C₂- to C₇-alkylene bridge may be fused with one, two or three aryland/or hetaryl groups, it being possible for the fused aryl and hetarylgroups each to carry 1, 2 or 3 substituents which are selected fromalkyl, cycloalkyl, aryl, alkoxy, cycloalkoxy, aryloxy, acyl, halogen,trifluoromethyl, nitro, cyano, carboxyl, alkoxycarbonyl and NE¹E², whereE¹ and E² are identical or different and are each alkyl, cycloalkyl oraryl, R¹ and R^(1′), independently of one another, are each alkyl,cycloalkyl, aryl or hetaryl, each of which may carry 1, 2 or 3substituents which are selected from alkyl, cycloalkyl and aryl, R² andR^(2′), independently of one another, are each alkyl, cycloalkyl, arylor hetaryl, it being possible for the aryl and hetaryl groups each tocarry 1, 2 or 3 substituents which are selected from alkyl, cycloalkyl,aryl, alkoxy, cycloalkoxy, aryloxy, acyl, halogen trifluoromethyl,nitro, cyano, carboxyl, alkoxycarbonyl and NE¹E², where E¹ and E² mayhave the abovementioned meanings, or a salt or mixture thereof.
 2. Thecatalyst composition as claimed in claim 1, A being a radical of theformulae II.1 to II-5

where X is O, S or NR⁵, where R⁵ is alkyl, cycloalkyl or aryl, or X is aC₁- to C₃-alkylene bridge which may have a double bond and/or an alkyl,cycloalkyl or aryl substituent, wherein the aryl is optionallysubstituted by one, two or three substituents, which are selected fromalkyl, alkoxy, halogen, trifluoromethyl, nitro, alkoxycarbonyl andcyano, or X is a C₂- or C₃-alkylene bridge which is interrupted by O, Sor NR⁵, and R³, R^(3′), R^(3″), R^(3′″), R⁴, R^(4′), R^(4″) and R^(4′″)independently of one another, are each hydrogen, alkyl, alkoxy, halogen,trifluoromethyl, nitro, alkoxycarbonyl or cyano.
 3. The catalystcomposition as claimed in claim 1, R¹ and R^(1′), independently of oneanother, being alkyl or aryl.
 4. The catalyst composition as claimed inclaim 1, R² and R^(2′), independently of one another, each being phenylsubstituents which may have one or two substituents which are selectedfrom alkyl, alkoxy, halogen, trifluoromethyl, nitro, cyano,alkoxycarbonyl and carboxyl.
 5. The catalyst composition as claimed inclaim 1, the phosphonite ligand of the formula I being selected fromligands of the formulae Ia to Ic

where, in the formula Ia, R³, R⁴, R⁷ and R⁸ have the following meanings:R³ R⁴ R⁷ R⁸ H H H H tert-butyl methyl H H tert-butyl methoxy H H H Hmethyl H H H ethyl H H H isopropyl H H H tert-butyl H H Cl H H H CF₃ H HH H methyl methoxy

in the formula Ib, R⁴, R⁷, R⁸ and R⁹ have the following meanings R⁴ R⁷R⁸ R⁹ H H H H Cl H H H methoxy H H H H H H phenyl H methyl H H H methylmethoxy H H methyl methoxy phenyl

in the formula Ic, R⁷ and R⁸ have the following meanings: R⁷ R⁸ H Hmethyl H ethyl H isopropyl H tert-butyl H methyl methoxy i-propyl Hi-propyl methoxy H Cl H CF₃


6. The catalyst composition as claimed in claim 1, which additionallyhas at least one further ligand selected from cyanide, halides, amines,carboxylates, acetylacetone, arylsulfonates, alkanesulfonates, hydride,CO, olefins, dienes, cycloolefins, nitriles, N-containing heterocycles,aromatics and heteroaromatics, ethers, PF₃ and mono-, bi- andpolydentate phosphine, phosphinite and phosphite ligands.
 7. Thecatalyst composition as claimed in claim 1, the metal of group VIIIbeing cobalt, rhodium, ruthenium, palladium or nickel.
 8. A phosphoniteligand of the formula I

as defined in claim 1, where R² and R^(2′), independently of oneanother, are each alkyl, cycloalkyl, aryl or hetaryl, it being possiblefor the aryl and hetaryl groups each to carry one or two substituentswhich are selected from alkyl, cycloalkyl, aryl, alkoxy, cycloalkoxy,aryloxy, acyl, halogen, trifluoromethyl, nitro, cyano, carboxyl,alkoxycarbonyl and NE¹E², where E¹ and E² are idendical or different andare each alkyl, cycloalkyl or aryl.
 9. A process for the preparation ofa mixture of monoolefinic C₅-mononitriles having a nonconjugated C═C andC≡N bond by catalytic hydrocyanation of butadiene or of a1,3-butadiene-containing hydrocarbon mixture, wherein the hydrocyanationis carried out in the presence of a catalyst composition as claimed inclaim
 1. 10. A process for the catalytic isomerization of branchedaliphatic monoalkenenitriles having a nonconjugated C═C and C≡N bond togive linear monoalkenenitriles, wherein the isomerization is carried outin the presence of a catalyst composition as claimed in claim
 1. 11. Aprocess for the preparation of adipodinitrile by catalytichydrocyanation of a linear monoolefinic C₅-mononitrile, wherein thehydrocyanation is carried out in the presence of a catalyst compositionas claimed in claim
 1. 12. A process for the preparation ofadipodinitrile, comprising a) preparation of a mixture of monoolefinicC₅-mononitriles having a nonconjugated C═C and C≡N bond by catalytichydrocyanation of butadiene or of a 1,3-butadiene- containinghydrocarbon mixture, b) catalytic isomerization of the mixture from a),and c) catalytic hydrocyanation of the isomerized mixture from b),wherein the steps a), b) and c) are carried out in the presence of atleast one catalyst composition as claimed in claim 1 and withoutisolation of the product or products from step a) and/or b).
 13. Aprocess for the hydrocyanation and/or positional and double-bondisomerization of olefins, wherein the hydrocyanation and/or positionaland double-bond isomerization of olefins is carried out in the presenceof a catalyst composition as claimed in claim
 1. 14. The catalystcomposition as claimed in claim 3, wherein R¹ and R^(1′), independentlyof one another, are selected from the group consisting of phenyl,